package test2;

public class demo56 {
    class Solution {
        public int numTrees(int n) {
            int[] dp = new int[n+1];
            dp[0] = 1;
            dp[1] = 1;
            for(int i = 2;i<=n;i++)
                for(int j = 0;j<i;j++)
                    dp[i]+=dp[j]*dp[i-j-1];

            return dp[n];
        }
    }
}
